Driving in wind vs. calm: which is more efficient and why?

[SVOboy]

What's more efficient and why: driving a round trip in calm conditions, or driving into a headwind at higher load, then in the tailwind on the return trip?

Thanks for the thoughts,

[wagonman76]

My thoughts are that calm would be better. Because the amount of work to power through the wind goes up exponentially as the speed increases. So the headwind (essentially higher wind speed) would hurt more than the gains youd get from a tailwind (essentially lower wind speed).

[Tango Charlie]

IF the gale was strong enough to put your vehicle's engine into an ideal load condition; i.e.-that elusive BSFC map island...
AND you could coast all the way home...
essentially a mega pulse and glide, then yeah, it would be more efficient.

In other words, I think calm conditions would win. Darn fickle Mother Nature...

[basjoos]

Calm. Most of the time you're not getting a pure head or tail wind and there is some crosswind component. The more of a crosswind vector you get, the more of a side load you're putting on your tires (the equivalent of light cornering with its increased RR) and vehicles typically have much worse Cd for a wind coming in at an angle than they do for a wind coming from straight ahead (increased aero drag). Then there's the exponential wind velocity factor mentioned above. But even if you drop your ground speed to compensate for the increased airspeed during the headwind portion of your drive and increase your groundspeed while driving in a tailwind, the crosswinds and gusts are still going to increase your RR and aero drag.

[trebuchet03]

Originally Posted by Tango Charlie

IF the gale was strong enough to put your vehicle's engine into an ideal load condition; i.e.-that elusive BSFC map island...

I'm not convinced that would be beneficial...

BSFC islands show you the best thermally efficient zones - but that doesn't mean it won't consume less fuel.

If riding in a headwind puts you into peak BSFC, you're using the least amount of fuel per HP... But, if you need to make 15hp more to be on that island, that could very well mean you're consuming more fuel, just at a higher thermal efficiency.

[aspera]

Doesn't your frontal area increase in a crosswind? The 'front' of your car is relative to the wind vector, not the vehicle's direction down the road.

[MetroMPG]

aspera: yes.

A goes up for sure; Cd probably does too.

[Otto]

Disturbed air might come as a tailwind, in which case drag would be lower.